Rear camera dilemna.....maybe

Just bought a twin rear view camera setup, and have realised there may be a problem.
The ideal area above the rear doors (Transit) is a sealed body section, i.e., the roof at that point is double skinned, so no access to route cables or bolt the unit down.
So I reckon the only place I can logically mount the cameras is on the door(s) themselves.

My question is - will the constant shutting of the doors harm the cameras in any way? And if they are mounted on some sort of shock absorbing material, will this affect the rear vision with wobble?

You could thread the necessary wires through a hole drilled through both skins, you only need access from one side to fit a grommet. The camera could be fitted with self tappers or if that's not strong enough, expanding bolts as used in stud walling.